This invention relates to a keyboard type electronic musical instrument which is controlled by time division. More particularly, it relates to an electronic musical instrument in which parallel signals of timings corresponding to respective notes of a keyboard are generated and transmitted to respective key switch circuits of the keyboard and in which a sum of note assignment signals (key depression signals) designated by key depression operations is taken by an OR circuit so as to transmit the signals to note or chord detection means in the form of serial timing signals.
An electronic musical instrument provided with a keyboard generates musical sounds in such a way that signals produced by depressing keys are processed in an electronic circuit. There are also electronic musical instruments which can, not only play the melody, but also generate chords or bass tones by operating an accompanying keyboard or a pedal keyboard. In recent years, there have also been developed electronic musical instruments in which a chord and a bass tone are automatically played in rhythmic accompaniment merely by depressing a single key on an accompanying keyboard or in which an automatic accompaniment is effected by a chord played on an accompanying keyboard and a bass tone adequate thereto. In such electronic musical instruments, as functions to be possessed become greater in diversity and higher in degree, circuit arrangements naturally become more complicated. In order to enhance the reliability and maintainability of apparatus and to achieve the reduction of cost, it is indispensable to put principal circuit blocks into the form of an LSI. In general, the cost of an LSI is dependent upon the price of a package, in other words, the number of pins at the time of mass production. Therefore, the circuit system of the electronic musical instruments needs to be suitable for the form of the LSI.
In the prior-art electronic musical instruments, the keyboard portion and the electronic circuit side are connected by signal lines corresponding to the respective notes of the keyboard so that key depression signals (tone assignment signals) may be entered onto the electronic circuit side in parallel. For this reason, the same number of signal lines as the number of the notes are required every sort of keyboard. That is, the keyboard portion and the electronic circuit side must be interconnected by signal lines in a number which corresponds to the product between the number of the sorts of the keyboards and the number of the notes. This makes the number of input terminals on the electronic circuit side very large, and the fabrication in the form of an LSI difficult.